1. Field of the Invention
The present invention relates to an antistatic film installed in an airtight vessel containing an electron source of an electron-generating device such as a picture display unit, to a spacer using such film, and to the picture display unit.
2. Related Background Art
A flat display unit using an electron-emitting device has, as shown in Japanese Patent Application Laid-Open No. H10-284286, a spacer, also called a rib, installed therein, which serves as a structural support resistant to ambient pressure for keeping the inside of the unit at a high vacuum.
FIG. 7 is a cross-sectional schematic view of an image-forming apparatus using many electron-emitting devices. Reference numeral 101 denotes a rear plate, reference numeral 102 a sidewall and reference numeral 103 a faceplate, and an airtight vessel is formed by the rear plate 101, the side wall 102 and the face plate 103. A spacer 107b that is a structural support resistant to ambient pressure in the airtight vessel has a low-resistivity film 110 thereon, and is connected to wiring 109 through an electroconductive frit 108.
An electron-emitting device 104 is formed on a rear plate 101, and a phosphor 105 and a metal back 106 are formed on a face plate. The objects of providing a metal back 106 include: to improve a utilization factor of light by minor-reflecting a light emitted from a phosphor 105; to protect the phosphor 105 from the collision of negative ions; to work as an electrode for applying an electron beam-accelerating voltage; and to work as a conducting path for electrons after having excited the phosphor 105.
A spacer 107a shows the electrostatically charged state of the spacer, and shows a state in which electrostatic charge (positive electrostatic charge in the drawing) is caused by collision of a portion of the electrons emitted from an electron source around it. Here, the spacer 107a shows the electrostatically charged state of the spacer when having no antistatic film 112 installed thereon, and thus, the thickness of a low-resistivity film is drawn more thickly than the low-resistivity film 110 contacting the antistatic film 112 of the spacer 107b, for convenience in illustration.
When a spacer 107a is positively charged with electricity as described above, electrons emitted from an electron-emitting device 104 being used an electron source are drawn toward the spacer, for example, like an electron trajectory 111a, and consequently impair the quality of a displayed image.
In order to solve this problem, there is a proposition of arranging an antistatic film 112 on a spacer 107b, eliminating the charge by passing a micro-electrical current through the surface, and thereby making electrons follow a predetermined trajectory such as an electron trajectory 111b, without being drawn to the spacer. There is also a proposition, as shown in Japanese Patent Application Laid-Open No. 2001-143620, of providing unevenness on the surface of a spacer glass substrate to reduce the effective secondary emission coefficient below that observed with a flat spacer surface, and effectively to inhibit the electrostatic charge of the spacer surface.
Furthermore, Japanese Patent Application Laid-Open No. H10-284283 proposes a spacer coated with an electrostatic charge-mitigating film containing aluminum nitride or aluminum oxide, and noble metals such as gold, palladium and platinum, by binary simultaneous sputtering with the use of an aluminum target and a noble metal target, and of a mixed gas of argon and nitrogen or oxygen as a gas for forming a film.
However, it has become clear that the spacers shown in the above described conventional examples cause variation in the performance of the function for eliminating electrostatic charge.
In particular, when a temperature distribution is formed in the spacer, the distribution of resistivity is also formed due to the temperature characteristic of the resistivity of the antistatic film. The variation of resistivity leads to variation in the diselectrification function.
Specifically, in a flat display panel, the instability of a display image results from temperature distribution in a panel plane, which is caused by a temperature difference between a face plate and a rear plate.
In addition, a conventional method of forming an antistatic film containing a plurality of elements by sputtering simultaneously a plurality of different material targets (for example, binary sputtering with the use of two materials) might cause variation in the resistivity of an antistatic film depending on each film-forming batch even when film-forming conditions (background, sputtering pressure, gas flow rate and target electrification power) are uniformized.
In order to uniformize resistivity, the target electrification power supplied to different material targets must be adjusted for each, which is complicated, and the operation is not always highly reproducible. In particular, in binary sputtering, when there is a large difference in target electrification power from one target to another, so-called cross contamination can not be avoided, which is a phenomenon in which a more powerfully electrified target material deposits on the surface of a less powerfully electrified target material.